Rosalind Franklin's work paved the way for Watson and and Crick. She and her PhD student took the photo that showed the double helix. The scientist leading the team at the lab, Maurice Wilkins, showed the photo to Watson and Crick. He and Franklin did not work together, and she was hired while he was not there, under the impression she would be working alone. And so she did. Wilkins was not involved in the taking of the photo, yet he shared her private research with Watson and Crick.
This photo was the missing piece for them to understand the structure of DNA and Franklin was not credited for it at the time. Wilkins, meanwhile, received the Nobel prize with Watson and Crick despite the single biggest contribution that came from the lab being Franklin's photograph.
It's nearly impossible to overstate just how pivotal and important this photograph was. There was no theory or model at the time that would have gotten them to understanding DNA. This x-ray crystallography photograph was THE missing piece.
Watson, Crick, and Wilkins could have properly credited her at any time. They included her photograph in the paper, explained how important it was. She wasn't even mentioned. They effectively plagiarized her work and took the credit.
